1. Field of the Invention
The present invention relates generally to image reading apparatuses and particularly to image reading apparatuses reading an original while transporting it.
2. Description of Related Art
Conventionally digital copiers and similar image reading apparatuses employ a technique referred to as so-called “reading an original while passing the original.” More specifically, an original is transported relative to a fixed line sensor in a sub scanning direction orthogonal to the line sensor as the original is read.
Such image reading apparatus is provided with a transparent platen between the original and the line sensor to fix a position at which a transported original is read. The original reflects light which is in turn received via the platen by the line sensor.
As such, if dust, paper particles, flaws or other similar foreign matters (hereinafter generally referred to as “dust”) adhered on the platen's reading position, the line sensor will read the dust while reading a transported original. This provides an output image with noise in the form of a line in the sub scanning direction.
Japanese Laid-Open Patent Publication No. 2000-278485 describes an image reading apparatus that detects noise caused by dust adhering on a platen glass's reading position from a read image by oscillating the platen in a main scanning direction as the apparatus reads an original. This image reading apparatus detects a specific waveform appearing in an image as noise generated by reading dust.
The image reading apparatus described in Japanese Laid-Open Patent Publication No. 2000-278485, however, employs pattern-matching to detect the specific waveform appearing in an image. As such, if an original includes such a pattern, the apparatus would erroneously detect the pattern.